Zoom lenses of a five-group construction are known. For example, Japanese Laid-Open Patent Application H10-268193, Japanese Laid-Open Patent Application 2000-292701, and Japanese Laid-Open Patent Application 2001-004919 disclose zoom lenses that include, in order from the enlarging side, a first lens group having negative refractive power and a focusing function and that is stationary during zooming, a second lens group having positive refractive power, a third lens group having positive refractive power, a fourth lens group having negative refractive power, with the second, third, and fourth lens groups being movable for zooming, and a fifth lens group having positive refractive power that is fixed during zooming.
There has been a demand for a zoom lens of the type described in these Japanese published applications that provides a bright image even with a liquid crystal image source in a projection display device and that has the compactness desired in a projection display device. In addition, recently there has been a demand for projection to a large screen at a close distance by using a projection lens with an even wider field angle. Moreover, a larger zoom ratio has been desired.
Furthermore, it is desirable that the zoom lens be at least nearly telecentric on the reducing side and include a large enough back focus distance to provide room for a color synthesizing optical system in a projection display device or, similarly, a color separation optical system when the zoom lens is used in a camera.
However, the brightness of a zoom lens is determined by limitations of movement of lens groups close to the aperture stop. Accordingly, the zoom lenses have been designed so that the amount of movement of moving lens groups close to the aperture stop does not increase too much in order to obtain a large zoom ratio without impairing the brightness at the telephoto end of the zoom lenses, as set forth in the Japanese published applications listed above. This requirement has become a primary factor constraining the degrees of freedom in the lens design of the zoom lenses.
The present invention relates to a zoom lens that includes five lens groups, three of which move for zooming, that allows the degrees of freedom in design to achieve a bright image, with a large zoom ratio and with a large amount of movement of lens groups close to the aperture stop, and that favorably corrects aberrations. Moreover, the present invention relates to a projection display device, such as a projection-type television, using such a zoom lens with, for example, a liquid crystal image source, and to a camera using an image pickup element, such as a CCD, an image pickup tube, photographic film, or similar devices, that uses such a zoom lens.